This invention relates to a display device comprising an electro-optical display medium positioned between two supporting plates, a system of pixels arranged in rows and columns, with each pixel being defined by two picture electrodes arranged on the facing surfaces of the supporting plates, a system of row and column electrodes for driving the pixels, at least one first asymmetrical non-linear switching element being arranged in series with each pixel between the pixel and a row electrode.
A display device of this type is suitable for displaying alphanumerical information and video information by means of passive electro-optical display media such as liquid crystals, electrophoretic suspensions and electrochromic materials.
A display device of the type described in the opening paragraph is known from Netherlands Patent Application no. 8701420 (PHN 12.154), which corresponds to U.S. Pat. No. 5,032,831 (July 1991). In a display device shown in this Application the pixels are given a certain adjustment for each row in that the capacitances associated with these pixels are accurately charged or discharged after they have first been discharged or charged too far (whether or not accurately). To this end such a picture display device is provided with means for applying, prior to selection, an auxiliary voltage across the pixels beyond or on the limit of the voltage range to be used for picture display.
In one of the embodiments this is effected by means of diodes which are connected to a suitably chosen reference voltage. A drawback of such a display device is that voltage lines must be provided between the pixels in the column direction for the reference voltage. Usually one or two column electrode(s) are alternately provided between the columns of pixels, namely one electrode for the reference voltage, two column electrodes, and so forth. Such a division is not only at the expense of the effective picture surface area, but also gives rise to artifacts in the picture.
A second drawback is that the picture electrodes, the column electrodes and the switching elements are realised on one and the same supporting plate, while the column electrodes, as well as the electrodes for the reference voltage, may be implemented as metal lines. The row electrodes are then provided on the other supporting plate and simultaneously constitute the counter electrodes of the picture electrodes. Therefore, these row electrodes are implemented as light-transmissive electrodes of, for example, indium tin oxide (having a width which is equal to the height of the picture electrodes). Such indium tin oxide electrodes usually have a high resistance so that accurate charging during one line period is not always possible.
Moreover, a so-called delta-colour filter configuration cannot be used without special measures in such a display device.
It is one of the objects of the present invention to provide a display device of the type described in the opening paragraph, which device has a large effective surface area and in which delta-colour filter configurations are readily applicable.
It is a further object of the invention to provide a display device in which an accurate adjustment of the pixels is possible.